Pro ess of separating gases



June 16, 1931.

R. L. HASCHE PROCESS OF S EPARATING GASES Fi'led May 5, 1928 6] emtoz Patented June 16, 1931 UNITED STATES RUDOLPH LEONARD HRSCHE, F ELIZABETH, NEW JERSEY, ASSIGNOR TO AMERICAN PATENT OFFICE SMELTING AND REFINING COMPANY, OF NEW YORK, N. Y., A CORPORATION 01 NEW JERSEY PRO'T'ESS OF SEPARATING GASES Application filed May 5, 1928. Serial No. 275,391.

This invention relates to the separation of gases, and more particularly to a continuous' process of separating .and recovering sulphur dioxide from a IlllXiJIG of furnace 5 gases by refrigeration and liquefaction under pressure.

In accordance with the present inv-ntion the furnace gases after being suit-ably cleaned. and compressed are cooled to elim- 1o iuatc the moisture content and subsequently further cooled to a degree sufficient to liquefy the sulphur dioxide and separate the same from the remaining gases which remain throughout in a gaseous state. The heat of vaporization of sulphur dioxide is returned to thesyst m to supply a portion of the cooling medium '1' or refrigeration. The

-major part of the refrigeration is obtained by expanding compressed, stripped gases in an expanding engine and there is also recovered in this operation a part of the original work of con'iprcssion which may be utilized for driving any desired pieces of apparatus. Means is also providedfor reventing the expanding engine from freezing whereby a continuous process is obtained. By a suitable arrangement of heat exchangers the refrigerating properties contained in the various gases by virtue of their sensible heat are retained within the system..

The invention further consists in the new and novel features of operation and the new and original arrangements and combinations of steps in the process hereinafter described and more particularly set forth in the claims.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, 4 as to its objects and advantages, the mode of its operation and the manner of its organization may be better understood by re ferring to the following description taken in connection with the accompanying drawings forming a part thereof, in which the figure is a diagrammatic representation of an arrangement of apparatus for effecting the various steps of the rocess.

The process in genera comprises purifying and compressmg the smelter gases for the elimination of materials which would' cooled while still under pressure to a temperature at which the sulphur dioxide becomes liquid, as, for example, a temperature of "0 C. The liquid sulphur dioxide is then vaporized and utilized as a cooling medium for certain of thesteps prior to its final recovery.

The stripped gases, freed from the'sulphur dioxide, are also utilized as a cooling medium and may be caused to absorb heat until their temperature approaches atmospheric. They are then passed through an adsorbing bed wherein the last traces of sulphur dioxide are removed and are applied to an expansion engine and allowed to expand from their initial high pressure down to a pressure slightly above atmospheric. The act of expansion further cools these gases and they are then passed through the heat exchange devices and assist in the various steps of cooling, after which they are vented into the atmosphere. I

Referring to the process more in detail, the mixture of smelter gases passes through a suitable cleaning system, such as a plurality of bag filters, and is cooled to approximately atmospheric temperature in suitable water cooling devices. The gas is then compressed to a comparatively high pressure, such as 15 atmospheres, and is passed through water cooled coils to remove the heat of compression and thence into suitable separators, such as the well known centrifugal separators, for eliminating the moisture condensed as a result of the compression, and any oil which may have carried over mechanically.

able means.

In order to eliminate the remaining traces of moisture, the gases may then be passed throughdriers, as, for example, towers filled with'calcium chloride, a suitable number being employed to remove further traces of moisture, the number depending upon the particular condition obtained. On leaving the driers the gases are passed through cooling coils to remove heat which has previously been absorbed, and are passed to a heat exchanger in which they are cooled to a comparatively low temperature, as for example, 15 C. It has been found that about 15% of the sulphur dioxide iiithe incoming gases is condensed in this exchanger, and may be recovered in liquid form.

A further quantity of sulphur dioxide is condensed in a third heat exchanger, which may be placed directly below the second exchanger for the purpose of heat economy, wherein the gas is cooled to a temperature of approximately C., at which temrature more than 90% of the sulphur 'oxide will become condensed. Obviously the exact temperatures egxployed will depend upon the initial qu "tity of sulphur dioxide present in the furnace gases and upon the completeness with which it is desired to recover the same.

The liquid sulphur dioxide may be passed to the second heat exchanger and evaporated therein for furnishing the cooling medium, and withdrawn to a suitable compressor by means of which it is compressed and stored for subsequent use. The suction produced by the compressor will normally be sufiicient to cause vaporization at a temperature below -l0 C., the boiling point of sulphur dioxide.

The stripped gases from the third heat exchanger which are of approximately the temperature thereof, or namely 70 C., are passed through the first heat exchanger and serve as a cooling medium therefor. After suiiicient heat has been absorbed by these gases to raise their temperature above their useful limit they may be again cooled by expansion." In expanding the gases with the production of external work, from a pressure of 15 atmospheres to approximately atmospheric pressure they may be cooled to a temperature at which sulphur dioxide becomes solid. 'It is preferable therefore to remove the last traces of sulphur dioxide prior to such expansion in order to prevent the expanding engine from becoming frozen with consequent interruption of service.

This may be accomplished by passing the stripped gases, prior to expansion, through a bed of material capable of adsorbing sul- .phur dioxide, for example silica gel or activated charcoal. The sulphur dioxide is thus completely removed and all danger of freezing the material in the expansion engine is eliminated.

A plurality of adsorbing bedsmay be employed, if desired for rendering the process continuous. \Vhen one bed is complete- 1y; saturated the gas stream ma then he s ifted to a secont bed and the irst rcactivated by any suitable means.

The stripped'gases free of sulphur dioxide are then applied to an ex ansion engine and expanded adiabatically rom an initial pressure of approximately 15 atmospheres to a pressure of approximately one atmosphere. The expanding engine may be used to run a compressor to compress fresh quantities of the purified smelter gases, or to compress the sulphur dioxide, or may be used to furnish power for other purposes.

The gas leaving the expanding engine is at a temperature below -100 C. and is passed through the jacket of the third heat exchanger and thence to the two sets of cooling coils, one following the calcium chloride driers, and the second set receding the first heat exchanger, after w ich it is vented into the atmosphere.

In this process the sensible and latent heat separated from the gases in the liquefaction of the sulphur dioxide has been returned to the system, and a large proportion of the work of compression is recovered in the expansion engine. It is obvious, therefore, that the process may be carried on continuously by the application of a minimum amount of power.

In the drawing forming a part of the present application, an apparatus has been shown in which the various steps thereof may be carried out. Referrin that drawing, the smelter gases, after bein subjected to suitable cleaning treatment and being compressed preferably to between 200 and 300 lbs. and cooled to atmospheric temperature, enter pipe 1 and pass through gas heat exchanger 2 and tube heat exchanger 3, wherein they are cooled to a temperature of approximately .0 C. and moisture collected as at 4 at the bottom of said heat exchanger. The gases are then passed through pipe 5 into suitable driers 6 and 7 which may contain calcium chloride or other suitable drying medium.

he gases, after passing through dricrs 6 and 7, in which the moisture has been commore particularly to 12 which may be placed directly under exchanger 11 and are cooled to the desired point, as for example, "0 C. 'while still under the above mentioned high pressure.

The liquid sulphur dioxide is thenrecovered as at 13 at the bottom of heat exchanger l2, and a portion thereof may be.

withdrawn into tank 14 to provide a reserve for cooling the heat exchangers when a sufficient amount of sulphur dioxide is not present in exchanger 12, as for example, in

starting the process. Valve 15 may be employed to control the passage of sulphur dioxide to tank 14..

Sulphur dioxide from the bottom of heat exchanger 12 is passed through pipe 16, controlled b valve 17, into heat exchanger 11 and is t ere vaporized for furnishing the cooling medium for said heat exchanger. The vaporized sulphur dioxide is then with drawn through pipe 18 to a suitable cornpressor (not shown) which delivers it in liquid condition to storage tanks.

[he stripped gases from exchanger 12 which are at a comparatively low temperature, such as (1., are removed upwardly through pipe 20 and applied to exchanger 3 for cooling the incoming gases. They are then passed through pipe 30 to adsorbers 31 and 32 which contain material suitable for removing the last traces of sulphur dioxide therefrom. as for example, silica gel or activated charcoal. Valves 33 and 34 may be employed to control the fiow of gas and selectively pass the same through the two jadsorb ers. When the gas is being passed through one adsorbcr the second may be reactivated as by passing steam or other hot. gases through pipes 35 embedded therein thereby heating the material and driving off the adsorber gas. Any other suitable reactivating means may be employed if de sired, the above being shown only as an example. After passing through adsorbers Ill or 32 the gases are removed through pipe 21, passed through reservoir 22 and applied to expansion engine 23. Valve 24 on reservoir 22 is used for regulating the pressure of the entire system, and in thc'cxample given above. would be set at slightly above 15 atmospheres.

The gases are expanded in engine 23 to approximately one atnmsphere and are thereby cooled to a temperature. somewhat. less than 100 (.7. At this temperature the sulphur dioxide would solidify had the last traces not been removed by the adsorption beds. The gases are then passed through pipe 25 and applied to heat exchanger 12 for cooling the sulphur dioxide gases to the liguefying point, as above mentioned. A ter passing through exchanger 12 they are withdrawn through pipe 26 and applied to gas exchanger 9, thence through pipe 27 to gas exchanger 2, thence through pipe28 to the atmosphere.

By means ofthe above described process and apparatus, sulphur dioxide gases may be readily removed from furnace gas and are recovered solely by the selective liquefaction. The etiiciency of the process. is maintained high by utilizing the cool gases at the various stages as a cooling medium for the different heat exchangers and also by applying the highl compressed gases to an expansion engine or recovering further quantities of power. The expansion engine not only serves to produce power, but also cools the gases to a sufficient degree to enable them to operate certain of the heat exchangers before being vented to the atmosphere.

By cooling the gases in various stages, the moisture is condensed and removed separately and prevented from subsequently interfering with the removal of the sulphur dioxide. The total number and size of driers depends upon the various materials used and the requirements of the particular case. The figures mentioned above are suitable for separating sulphur dioxide from smelter gases in which the content thereof is approximately 10% by volume. Obviously for other proportions of sulphur dioxide in the gasthe temperatures and pressures would be correspondingly changed. This may be effectively accomplished by means of control valve 24.

The use of adsorbing beds for eliminating traces of sulphur dioxide before applying the gases to the expanding engine renders the. process continuous since the material is prevented from freezing in the engine and interfering with the operation thereof. Any other suitable means of elimination may be employed however without depart-- ing from the scope of this invention.

A process has: been disclosed for case of description as applied particularly to smelter gases, but it is obviously capable of being applied to the separation of other gases from other combinations thereof and is not intended to be limited to the specific elements mentioned in the description.

Athough certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the several steps of the process and in its operation may be made by those skilled in this art withoutv departing from the spirit of the invention.

\Vhat is claimed is:

1. The continuous process of recovering sulphur dioxide from furnace gases which comprises compressing said gases removing moisture and other impurities from said compressed gases, cooling the same toapproximately .tl C. whereby a large portion of the remaining moisture is condensed, passing said gases through driers for removing the remainder of said moisture, cooling said gases in a plurality of stages to a temperature of approximately "70 C. whereby sulphur dioxide is liquefied removing the sulphur dioxide from contact with the stripped gases at said temperature, vaporizing the liquid sulphur dioxide and utilizing the heat of vaporization as a cooling me dium for one of said stages, withdrawing and recovering said vaporized sulphur. dioxide, withdrawing the stripped gases from the liquid sulphur dioxide, utilizing the same for cooling further quantities of incoming gases to approximately .0 C., removing traces of sulphur dioxide, expanding the stripped gases to slightly above atmospheric pressure, recovering work therefrom while expanding, utilizing the expanded gases as a heat exchange medium for furnishing the final cooling of the incoming gases, and further utilizin said expanded gases for cooling thev incoming gases during the initial stages of the process.

2. The process of recovering sulphur dioxide from gas mixtures such as gases from sulphur burners and by productfurnaces which comprises compressing said gases to a pressure substantially above atmospheric, removing the moisture from the compressed gases and cooling the gases to substantially the melting point of sulphur dioxide at the pressure involved removing the liquid sulphur dioxide from contact with the stripped gases at said temperature, then removing the remaining traces of sulphur dioxide from the stripped gases whereby said traces are prevented from freezing when the gases are further cooled and expanding said gases with the production of external work to further cool the same whereby the expanded gases may be utilized as a refrigerant'in the above cycle. i

3. The process of recovering sulphur dioxide from gas mixtures which comprises compressing said gases to substantially above atmospheric pressure, removing the moisture therefrom and cooling to approxi mately the melting point of sulphur dioxide at the pressureinvolvedwhereby a substantial portion of the sulphur dioxide is lique-' lied and removing said liquid from contact with the gas at said temperature, utilizing the stripped gas as a refrigerant for the incoming gases, removing remaining traces of sulphur dioxide therefrom whereby said traces are prevented from freezing out when the gases are further cooled, then expanding said gases with the production of external work whereby said gases are cooled below the melting point of sulphur dioxide and using said expanded gases as a refrigerant for cooling the incoming gases to approximately'the melting point of sulphur dioxide.

4. The. process of removing sulphur dioxide from gas mixtures which comprises compressing said mixtures and removing the moisture therefrom, cooling said mixtures to just above the melting point of sulphur dioxide at the pressure involved whereby a substantial portion of the sulphur dioxide is liquefied and removing said liquid from the gases, at said temperature, utilizing the evaporating sulphur dioxide and the stripped gases as refrigerants for the incoming gases, removing the last traces of sulphur dioxide from the stripped gases to prevent said traces from freezing out when the gases are further cooled and expanding said gases with the production of external work whereby they are cooled below the melting point of snlphurdioxide, and utilizing the expanded gases as a refrigerant for cooling the incoming gases to approximately the melting point of sulphur dioxide in the step above mentioned.

The proccss of removing sulphur dioxide trom gas mixtures which comprises compressing said mixtures and removing the moisture therefrom, cooling said mixtures to just above the melting point of sulphur dioxide at the pressure involved whereby a substantial portion of the sulphur dioxide is liquefied and removing said liquid from the gases atsaid temperature, utilizing the evaporating sulphur dioxide and the stripped gases as refrigerants for the incoming gases, removing the last traces of sulphur dioxide from the stripped gases to prevent said traces from freezing out when the gases are further cooled by passing said gases through beds of material capable of adsorbing sulphur dioxide, expanding said gases with the production of external work whereby they are cooled below the melting point of sulphur dioxide and utilizing the expanded gases as a refrigerant for cooling the incoming gases to approximately the melting point of sulphur dioxide in the step above mentioned.

6. The process of removing sulphur diox ide from gas mixtures which comprises compressing said mixtures and removing the moisture therefrom, cooling said mixtures to just above the -m elting point of sulphur dioxide at the pressure involved whereby a substantial portion of the sulphur dioxide is liquefied and removing said liquid from the gases at said temperature, utilizing the evaporating sulphur dioxide and the stripped gases as refrigerants for the incoming gases, removing the last traces of sulphur dioxide from the stripped gases to prevent said traces from freezing out when the gases are further too cooled by passing said gases through a bed of silica gel, expanding said gases with the production, of external work whereby the are cooled below the melting oint of s phur dioxide, and utilizing t e expanded gases as a refrigerant for cooling the incoming gases to approximately the melting point of sulphur dioxide in the step above men-v tioned.

In testimony whereof I have hereunto set my hand.

RUDOLPH LEONARD HASCHE. 

